1. Field of the Invention
The present invention relates to a three-dimensional image capturing device by which a three-dimensional shape of a measurement subject, which is to be measured, is captured by a time-of-flight measurement.
2. Description of the Related Art
A three-dimensional measurement using a three-dimensional image capturing device is classified as an active system, in which light, an electric wave or sound is radiated onto a measurement subject, and a passive system in which the light, electric wave or sound is not output. The active system comprises the time-of-flight measurement, a phase detection using a modulated light wave, a triangulation, a moirxc3xa9 topography, and so on, and the passive system comprises a stereo vision system, and so on.
An active system device is very bulky in comparison with that of the passive system, since the device requires a laser beam output mechanism. However, the active system device is superior regarding a distance measurement resolution, a measuring time, a measuring range and soon, and thus, despite the bulkiness, the device is utilized in various fields. In a three-dimensional image capturing device, described in xe2x80x9cMeasurement Science and Technologyxe2x80x9d (S. Christies et al., vol.6, p.1301-1308, 1995), a pulse-modulation laser beam irradiates a measurement subject, and a reflected light beam, which is reflected by the measurement subject, is received by a two-dimensional CCD sensor to which an image intensifier is attached, so that an image signal, corresponding to the reflected light beam, is converted to an electric signal. ON-OFF control of the image intensifier is carried out by a gate pulse, which is synchronized with the pulse radiation of the laser beam. According to the device, since an amount of received light, based on the reflected light beam from the measurement subject, which is positioned far from the device, is less than that of received light based on a reflected light beam from a measurement subject, which is close to the measurement subject, an output corresponding to a distance between the measurement subject and the device can be obtained for each pixel of the CCD.
Therefore, an object of the present invention is to provide a three-dimensional image capturing device by which a three-dimensional shape of a measurement subject is sensed with high accuracy.
According to the present invention, there is provided a three-dimensional image capturing device, comprising a light source, a plurality of photoelectric conversion elements, a signal charge holding unit, an electric charge discharging processor, a signal charge transfer processor, signal charge integrating processor and an error sensing processor.
The light source irradiates a distance measuring light beam to a standard subject, to which the distance from the device to a surface of the standard subject is known, and a measurement subject, to which the distance from the device to a surface of the measurement subject is unknown. The distance measuring light beam is a pulsed beam and the measurement subject reflects the distance measuring light beam to generate a reflected light beam pulse. The plurality of photoelectric conversion elements receive the reflected light beam pulse from the standard subject and the measurement subject, so that an electric charge corresponding to an amount of the received reflected light beam is accumulated in each of the photoelectric conversion elements. The signal charge holding unit is disposed adjacent to each of the photoelectric conversion elements. The electric charge discharging processor discharges unwanted charge accumulated in each of the photoelectric conversion elements, so that an accumulating operation of signal charge is started in each of the photoelectric conversion elements. The signal charge transfer processor transfers the signal charge accumulated in the photoelectric conversion elements to the signal charge holding unit. The signal charge integrating processor drives the electric charge discharging processor and the signal charge transfer processor alternately to integrate the signal charge in the signal charge holding unit, so that distance information, corresponding to the distance from the device to the surface of each of the standard subject and the measurement subject, is sensed. The error sensing processor senses an error of the distance information to the measurement subject, based on the signal charge integrated in the signal charge integrating processor when using the standard subject.